Furnace with combustion air source control



June 6, 1967 F. HARBIN FURNACE WITH COMBUSTION AIR SOURCE CONTROL Filed oct. 2o, 196e 2 Sheets-Sheet l fa. Z.

fiom( FURNACE WITH COMBUSTION AIR SOURCE CONTROL Filed Oct. 20, 1966 F. HARBIN June 6, 1967 2 Sheets-Sheet 2 United States Patent O 3,323,509 FURNACE WITH COMBUSTION AIR SURCE CONTROL Frank Harbin, Holland, Mich., assigner, by mesne assignments, to Lear Siegler, Inc., Santa Monica, Calif., a

corporation of Delaware Filed Oct. 20, 1966, Ser. No. 588,083 8 Claims. (Cl. 126-110) ABSTRACT F THE DISCLOSURE A safety means or method for a gun-type furnace for living quarters such as mobile homes and other small dwellings in which the air for combustion is drawn from outside the dwelling through the compartment in which the burner is located. The means or apparatus includes an air impervious door which permits access to the burner compartment for maintenance purposes but which with other structure completely encloses the compartment so that a-ir cannot be drawn from within the dwelling. Associated with the door is a switch means actuated by closing or opening of the door so that the burner means is rendered operative only when the door is closed. Within a narrower aspect of the invention the furnace has another door permitting access to the furnace blower and another switch is provided which in conjunction with the first switch permits operation of the burner only when both d-oors are open.

This invention lrelates to furnace constructions, and more particularly to a furnace construction featuring a new type of safety means which renders the furnace inoperative when predetermined dangerous conditions exist.

The furance construction of the present invention relates principally to oil-tired gun-type hot air furnaces used in mobile homes, inasmuch as specific safety problems have previously arisen in this area. Because mobile homes have relatively small air space volumes inside them and because they usually are very weather-tight and air-tight, the use of any furnace must be attended by considerable care since it is deceptively easy to take an excess famount of air from with-in the mobile home for supporting combustion within the furnace, thereby making breathing conditions `within the mobile home unsafe or harmful. This is particularly true of gun-type furnaces, since they require a great deal of air when burning.` It has for some time been the practice to mount such furnaces adjacent an outer wall of the mobilehome or trailer, where a vent in the burner compartment of the furnace may freely communicate with outside air available through a ventor louver in the outer wall, so that such air may be drawn into the burner compartment when the burner is operating. This precludes the use of inside air for combustion so long as the access doors into the interior of the furnace remain completely closed, as they normally are. Since it is entirely possible for such doors to inadvertently be left at least partially open, however,

a very real potential danger has nonetheless continued to ex-ist including the possible illness and death of the occupants of the mobile home due to oxygen deprivation and/'or air contamination.

In recognition of this inherent danger, the Underwriters Laboratories (UL) has recently set forth minimum safety standards for mobile home furnaces which include the requirement for a cowling which lits snugly around the air inlet of the burner and extends directly into a duct leading to the outside, such that even if the door of the burner compartment within the furnace is left lopen, no air from within the trailer can possibly be drawn into the burner and used for combustion. While such a provision is eminently satisfactory from a purely safety point of View, it is not satisfactory to furnace manufacturers, since it represents a very appreciable extra manufacturing expense which cannot readily be passed on to the consumer. Mobile homes, and consequently mobile home furnaces, are: becoming a highvolume commodity in the American economy, and the aforesaid extra expense would on an annual basis amount to a sizeable loss to the manufacturers involved.

In view of the foregoing circumstances, the present inventor has conceived of a novel alternate system for achieving the `desired safety `without incurring so undesirable an expense to the manufacturers involved. The system has been approved by the Underwriters Laboratories, and provides a unique and desirable solution to what has previously been a regrettable and undesirable set of circumstances.

Accordingly, it is a major object of the present invention to provide a new type of furnace.` construction which includes a system wherein lthe burner of the furnace is completely disabled or rendered inoperative whenever the door of the burner compartment in the furnace cabinet is open or partially open.

It is a further object of the invention to provide a furnace construction of the aforesaid nature, in which both the burner and the blower of the furnace are rendered inoperative if either the burner compartment door or the blower compartment `door is left open or partially open.

It is a further important object of the invention to provide a furnace construction of the aforesaid character in which the burner and blower will operate if both the burner compartment and blower compartment doors are open, but not if either one of them is open while the other is closed. This allows for normal servicing of the burner and blower, which can only take place while their respective compartment doors are open and while they are in operation. However, owing to typical installation conditions, both of these doors could not be open without obstructing the usual traic pattern within a mobile home, and consequently allowing the furnace to operate under these circumstances is quite acceptable as a matter of safety.

The foregoing major objects of the invention and the advantages provided thereby, together with other objects and advantages equally `a part thereof, will become increasingly apparent following consideration of the ensuing specification and its appended claims, particularly when taken in conjunction with the accompanying illustrative drawings setting forth a preferred embodiment of the invention.

In the drawings:

FIG. l is a frontal perspective of the furnace unit involved in the present invention;

FIG. 2 is a fragmentary sectional elevation showing details of the furnace cabinet, including the burner compartment and blower compartment doors located at the front of the cabinet;

FIG. 3 is an enlarged fragmentary sectional elevation showing a portion of the structure seen in FIG. 2;

FIG. 4 is an enlarged fragmentary sectional plan view of the structure seen in FIG. 3;

FIGURES Sato 5d are a series of schematic representations showing the different switching conditions which the system of the invention may assume at any one time in the operation of the furnace; and

FIG. 6 is a schematic circuit diagram of the control circuit for the furnace.

Briefly stated, the present invention provides a furnace construction which includes a cabinet structure defining mutually distinct internal compartments for a burner assembly, a heat exchanger, and blower. The furnace construction includes an electrically operated burner means located in the burner compartment, an electrically operated blower located in the blower compartment, and a control circuit which is connected to the burner and blower for operating the same. The cabinet structure defines doorway openings for the burner and blower compartments which permit access thereinto from outside the cabinet, and each such compartment has its own door member shiftably mounted thereupon to open or close the respective doorway openings. The invention then includes switch means mounted on the cabinet structure for actuation between rst and second switching conditions by the opening and closing of the aforesaid compartment door members. Circuit means connect the switch means into the `aforesaid control circuit, such that at least the burner means and preferably both it and the blower are maintained in an inoperative condition when any one of the door members is open and the other is closed. Further, the switch means and circuit means permit operation of the burner and blower when both of said doors are either open or closed, but only under these conditions.

Referring now in more detail to the drawings, the overall furnace construction is seen at in FIG. 1, and it will there be seen that a cabinet structure 12 illustrated in the form of a rectangular box denes mutually separated compartments 14, 16, and 18, termed respectively a blower lcompartment, a heat-exchanger compartment, and a burner compartment. While their specific form or type is not actually an integral part of the invention, it will be noted that a blower 15 is mounted in the blower compartment 14, a heat exchanger 17 is mounted within the heat exchanger compartment 16, and a burner means 19 is mounted within the burner compartment 18. While these compartments are said to be mutually distinct, they do, of course, communicate with each other, but only through definite and prescribed passages (not specically shown) l so that the different components may operate together as a furnace unit. However, it is very important that the combustion products from the burner 19 remain completely distinct from the heated air which the blower 15 circulates through the mobile home, and it is in this sense that the term mutually distinct compartments is used in the present specification and claims.

The blower 15 of the furnace construction operates by drawing air from within the trailer into the blower compartment 14 through a louvered or ventilated blower compartment door 20` and driving such air through the heat exchanger 17 into a plenum chamber 22 located at the base of the furnace, from which the heated air is ducted throughout the home or trailer in a desired manner. The burner means 19 of the furnace construction operates by drawing air through a vent passage 24 located in the bottom of the cabinet structure into the burner compartment 18, in the manner shown by the arrows in FIGS. 1 and 2. From the burner compartment, this air is drawn into the burner means 19, :and used for combustion, which takes place within the connes of the heat exchanger 17. This, of course, heats the heat exchanger so that air impelled over it by the blower 15 is heated thereby. The combustion products and gases pass from the combustion chamber within the heat exchanger out a typical vent or stack 26 at the top of the cabinet structure, which communicates with the combustion chamber therewithin. As illustrated in FIG. 1, the burner compartment 18 has a door 26 which closes a doorway defined by the compartment adjacent the burner means 19, at the front of the cabinet structure.

The blower compartment door 20 and the burner compartment door 26 are seen in more detail in FIGS. 2, 3 and 4. Blower compartment door 20 is hinged to the cabinet structure 12 at 28 and 30 so that it may be swung open to provide access into the blower chamber 14. The burner compartment door 26 is preferably detaehably mounted on the cabinet structure through a lock assembly 32, comprising a latch plate 34 secured to a rotatable shaft 36 which extends through the door 26 and is accessible from outside the cabinet structure. Thus, door 26 may be removed from the burner compartment 18 by rotating shaft 36 and lifting the door outwardly.

Inside the cabinet structure, a horizontally oriented partiton or panel 38 divides the blower compartment 14 from the burner compartment 18 near the front of the cabinet structure, and it is upon partition 38 that the switch means 40 of the present system is mounted, immediately adjacent the lower part of blower compartment door 20 and the upper part of the burner compartment door 26. A power supply junction box 42 mounts inside the blower compartment 14 and receives inlet line power, which connects to the switch means 40 through a cable 44. Also, power is coupled from the switch means 40 through a cable 46 to an internal power supply junction box 48, into which a line from the burner means 19 connects.

The switch means 40 comprises a mounting box or enclosure 41 (FIGS. 3 and 4) which houses a pair of single pole-double throw electrical switches 56 and 52. Each such switch has an outwardly-extending actuating member or plunger 51 and 53, respectively, which extends outwardly through the switch enclosure 41 and contacts the inner face of the doors 20 and 26, respectively. In their fully closed positions, each of the doors hold their `respective plungers or switch-actuating elements 51 and 53 inwardly, whereas when either door is opened, it releases its associated plunger. Actuating members or plungers 51 and 53 are spring-loaded inside switches 50 and 52 such that when they are not held in, the :plungers move outwardly and cause switching actuation of their associated switches 50 and 52. That is, when the plungers are held inward, they cause a first switching condition of the associated switches, and when the plungers move out, they cause a second switching condition. This is illustrated electrically in FIG. 5, wherein both switches 50` and 52 are shown, together with interconnecting circuitry 56, including power-in leads 58 and power-out leads 59, by which the switch means is coupled into the control circuit for the furnace (illustrated in FIG. 6 and discussed subsequently).

As seen in FIGURES 5a to 5d, each of the switches 50 and 52 has an internal movable switch arm labeled 60 and 62, respectively, which moves from a position contacting a lower switch contact to a position contacting an upper switch contact upon inward depression of the associated plungers 51 and 53 of each switch. Since there are two switches and each switch has two possible switching conditions, a total of four situations are possible. These are illustrated in FIGS. 5a, 5b, 5c, and 5d, respectively.

In FIG. 5a, both plungers 51 and 53 are extended, as would be the case when both the blower compartment door 20 and the burner compartment door 26 are open. Under these circumstances, both movable switch arms 60 and 62 are in contact with the lower set of switch contacts in each of the switches 50 and 52. Consequently, power supplied to inlet leads 58 had a closed path through the switch arms 60 or 62 and conductor 56h, so that power is present at the output leads 59.

FIG. 5b shows the situation existing when the blower compartment door 20 is closed but the burner compartment door 26 is open. Here, plunger 51 of switch 50 is depressed, while plunger 53 of switch 52 is extended. Power from inlet leads 58 thus passes through the upper contact in switch 50 and is present on lead 56a, ibut is not coupled through switch arm 62 to the output leads 59. Consequently, no power passes through the switch 40 under this condition.

FIG. 5c shows a situation existing when the blower compartment door 20 is open and the burner compartment door 26 is closed. Here plunger 51 remains extended, whereas plunger 53 is depressed. This provides the converse of the situation seen in FIG. 5b, i.e., power from leads 58 passes through switch arm 60 and is present on conductor 56h, but is not connected through switch arm 62 to the output leads 59. Consequently, no power passes through the switch means 40 in this condition.

` nace construction is shown in FIG. 6 to illustrate both the interconnection and the interaction therewith of the switch means 4t) of the invention. Components seen in FIG. 6 are labeled with corresponding numerals seen in other tigures, to provide a more complete understanding of the total system. In the interest of completeness, certain components of the control circuit 70 are illustra-ted and labeled, but since these are conventional components and operate in the circuit in a conventional manne-r, a specilic discussion of them is not deemed necessary. Conventional line power is seen entering the control circuit 70 at the main junction box 42, whose location inside the cabinet structure 12 is shown in FIG. 2t. The cable 44 seen in FIG. 2 connecting junction box 42 with the switch means 40 is also shown, as is cable 46, which connects the switch means -to the junction box 48 supplying power to the burner means 19. Connections are also shown from the junction box 48 to the blower 15.

As shown in the preferred form in FIG. 6, the switch means 40 is thus located directly in the line power supply which operates both the blower 15 and the burner means 19. From the foregoing discussion of the four conditions seen in FIG. 5, it will be apparent that whenever both the blower compartment door 20 and the burner comparement door 26 are either opened or closed, the switch means completes a path into the junction box 48, so that the blower 15 and burner means 19 may operate normally. Consequently, both doors may be opened for service, but both doors must be securely closed for steady state operation of the furnace construction in a heating capacity. This satisfies the safety criteria discussed a-t the outset of this specification.

On the other hand, if either the blower compartment door 20 or burner compartment door 26 somehow becomes opened, so -that an inherently dangerous situation exists wherein the burner means could draw air from inside the mobile home or trailer for use in combustion, the switch means 40 will automatically prevent both the blower 15 and the burner means 19 from any operation whatsoever. Thus, safety conditions are fully maintained, even though the much more expensive ducting mentioned previously has been completely eliminated and the conventional furnace cabinet is utilized. In this connection, it should be noted that preventing the blower 15 from operating under either inherently dangerous condition (i.e., burner compartment door or blower compartment door open) is not as strict a necessity as for the burner means to remain inoperative during such condi-tions. Consequently, if desired, the switch means 40 may be connected into the control circuit 70 between the junction box 48 and the burner means 19. This will allow the blower 15 to operate a-t all times, but provide the same operation for the burner means as already described.

Thus, the present invention will immediately be seen to provide a very complete answer for the unsafe conditions which have previously caused alarm in the mobile home industry, while nonetheless eliminating the need for the expensive ducting of the burner means described above. As stated, the present system has been accepted by the UL as satisfactory, and its economy when compared to the added ducting will be manifest.

It is entirely conceivable that upon examining the foregoing disclosure, those skilled in the art may devise embodiments of the concept involved which dilfer somewhat from the embodiment shown and described herein, or may make various changes in structural details to the present embodiment. Consequently, all such changed embodiments or variations in structure as utilize the concepts of the invention and clearly incorporate the spirit thereof are to be considered as within the scope of the claims appended herebelow, unless these claims by their language specifically state otherwise.

I claim:

1. A furnace construction, comprising in combination: a cabinet structure deiining mutually distinct internal cornpartments for a burner assembly, a heat exchanger, and a blower; an electrically operated burner means located in said burner compartment; an electrically operated blower located in said blower compartment; a control circuit connected to said burner means and blower for operating the same; said cabinet defining doorways for said burner and blower compartments permitting access thereinto from outside the cabinet; a first door member shiftably mounted on said cabinet to open and close said burner compartment doorway; a second door member shiftably mounted on said cabinet to open and close said blower compartment doorway; switch means mounted on said cabinet structure; said switch means being actuated between rst and second switching conditions by the opening and closing of said compartment door members; and circuit means connecting said switch means into said control circuit such that said burner means is maintained in an inoperative condition when one of said door members is open and the other is closed and said burner means is operative only when both of said doors are open or closed.

2. The furnace construction recited. in claim 1, wherein said circuit means connects said switch means into said control circuit such that both said burner means and said blower are maintained in an inoperative condition when one of said door members is open and the other is closed and rendered operative only when both of said doors are open or closed.

3. The furnace construction recited in claim 1, wherein said switch means .includes a pair of actuating elements extending outwardly therefrom to a position wherein each such element is in close proximity with only one of said door members when the same are in a closed position, said switch means being actuated to another switching condition by movement of either of said door members away from its respective actuating element.

4. The furnace construction recited in claim 3, wherein said switch means comprises iirst and second individual switch components, each having one of said actuating elements, and wherein said elements comprise movable plungers contacting said door members when the same are closed.

5. The furnace construction recited in claim 4, wherein both of said switch components are single pole-double throw electrical switches.

6. The furnace construction recited in claim 5, wherein said circuit means connects said switches into said control circuit such that both said burner means and said blower are maintained in an inoperative condition when one of said door members is open and the other is closed and rendered operative only when both of said doors are open or closed.

7. A furnace construction, comprising in combination: a cabinet structure defining mutually distinct internal compartments for a burner assembly, a heat exchanger, and a blower; said burner compartment communicating with a source of air for combustion, an electrically operated burner means located in said burner compartment and drawing its combustion air therefrom; an electrically operated blower located in said blower compartment; a control circuit connected to said burner means and blower for operating the same; said cabinet defining at least one doorway for said burner compartment permitting access thereinto from outside the cabinet; an air-impervious door member shiftably mounted on said cabinet to open and close said burner compartment doorway to completely encase said burner compartment and shut off flow of air through said doorway when the door is closed; switch means mounted on said cabinet structure, said switch means being actuated between first and second switching conditions by the opening and closing of said c0mpart ment door member; -and circuit means connecting said switch means into said control circuit such that said burner means is maintained in an inoperative condition when said door member is open and said burner means is operative only when said door is closed.

8. A method of preventing the burner means in a guntype furnace from drawing air from the living quarters which such furnace is being used to heat through an aco cess doorway to a compartment through which said burner is designed to draw air for combustion, comprising the steps of; completely enclosing said burner compartment by means of a structure including an air impervious door which when fully closed will completely close said doorway and prevent air from being drawn therethrough; sensing the position of said door; and disabling said burner means from operating when said door assumes a position other than a fully closed one.

References Cited UNITED STATES PATENTS 2,130,491 9/1938 Gilliland 158-42.1 X 2,284,674 6/1942 Murdock 126-110 X 2,538,492 l/1951 Anderson et al. 15S-42.1 X

JAMES W. WESTHAVER, Primary Examiner. 

1. A FURNACE CONSTRUCTION, COMPRISING IN COMBINATION: A CABINET STRUCTURE DEFINING MUTUALLY DISTINCT INTERNAL COMPARTMENTS FOR A BURNER ASSEMBLY, A HEAT EXCHANGER, AND A BLOWER; AN ELECTRICALLY OPERATED BURNER MEANS LOCATED IN SAID BURNER COMPARTMENT; AN ELECTRICALLY OPERATED BLOWER LOCATED IN SAID BLOWER COMPARTMENT; A CONTROL CIRCUIT CONNECTED TO SAID BURNER MEANS AND BLOWER FOR OPERATING THE SAME; SAID CABINET DEFINING DOORWAYS FOR SAID BURNER AND BLOWER COMPARTMENTS PERMITTING ACCESS THEREINTO FROM OUTSIDE THE CABINET; A FIRST DOOR MEMBER SHIFTABLY MOUNTED ON SAID CABINET TO OPEN AND CLOSE SAID BURNER COMPARTMENT DOORWAY; A SECOND DOOR MEMBER SHIFTABLY MOUNTED ON SAID CABINET TO OPEN AND CLOSE SAID BLOWER COMPARTMENT DOORWAY; SWITCH MEANS MOUNTED ON SAID CABINET STRUCTURE; SAID SWITCH MEANS BEING ACTUATED BETWEEN FIRST AND SECOND SWITCHING CONDITIONS BY THE OPENING AND CLOSING OF SAID COMPARTMENT DOOR MEMBERS; AND CIRCUIT MEANS CONNECTING SAID SWITCH MEANS INTO SAID CONTROL CIRCUIT SUCH THAT SAID BURNER MEANS IS MAINTAINED IN AN INOPERATIVE CONDITION WHEN ONE OF SAID DOOR MEMBERS IS OPEN AND THE OTHER IS CLOSED AND SAID BURNER MEANS IS OPERATIVE ONLY WHEN BOTH OF SAID DOORS ARE OPEN OR CLOSED. 